U.S. Pat. No. 3,891,874, issued June 24, 1975, by Herbert C. Roters, inventor for a "Compensated Reciprocating Electrodynamic Machine"--assigned to Mechanical Technology, Incorporated of Latham, New York, describes a reciprocating electrodynamic linear motor of the type to which the present invention relates. Where linear reciprocating motors of the type described in U.S. Pat. No. 3,891,874 are used to provide the primary moving force in resonant free piston compressors of the type described in U.S. Pat. No. 3,937,600, issued Feb. 10, 1976, by Harlan V. White, inventor--entitled "Controlled Stroke Electrodynamic Linear Compressor," and in U.S. Pat. No. 4,067,667, issued Jan. 10, 1978, by Harlan V. White--inventor for a "Controlled Stroke Electrodynamic Oscillating Motor Compressor," both assigned to Mechanical Technology, Incorporated, certain inefficiencies are introduced by operating the linear reciprocating motor in the classical manner with a fixed magnitude DC field coil winding current over the complete operating range of the motor, as taught by U.S. Pat. No. 3,891,874. To overcome these inefficiencies the present invention was devised.